There's a big black hole in the middle of my Mines of Avarice map and I can't seem to uncover it. I've tried entering from the gated side in the canyon and from the dwarf fortress to no avail. I've tried hopping on the wall decorations, using the blue rune for extra melee power, solving the cube puzzle, and doing the other quests in the area. How do I uncover this last part?
Missing portion of map is near orange triangle in following map: